Strictly 75 nodes, one node being an isolated group of connected components, you get any connection to the "0" node for free. You can get a clue from the Output File, it lists the number of nodes in the circuit, and their names. There are some other restrictions as well, see the "demoswitch" documentation for more details. Exceeding the limits will reported in messages.

Wouldn't connecting R1 to R2 be a NODE? Same as connecting R1, R2 & R3 would create a Node. I could see connecting two nodes together with a component; that would be an entry in the NETLIST (e.g R1, N1, N2, 1k). Then virtually each component would correspond to a net. According to the limitations OrCad Lite can simulate 75 nets, but only save 60 components. The limitations say you can simulate up to 75 nodes, but it hard to see how this is possible with a 75 Net limit which is sure to be reached before the 75 node limit.